SM3414B

Optical Encoder IC

SM3414B Reflective Absolute Optical Encoder IC
Compact package:
Can be mounted in tiny spaces
Absolute position data: Outputs 9-bit absolute position at 100 μm resolution
Adjustment function: Built-in adjustment functions configurable via
serial interface

1. SM3414B Overview
The SM3414B is a compact encoder IC that integrates a LED light source and an OEIC (Opto-Electric Integrated
Circuit) in a small package for surface mounting and can output two-phase analogue signals and 9-bit absolute positiondata.
It employs an optical sensor array that greatly reduces signal degradation problems due to variations in mounting
position. It delivers high-accuracy position detection even when mounted using reflow methods. It is ideal for various
applications that require the following features.
[Features]Miniature clear molded package 7.7mm (W) × 6.4mm (L) × 1.0mm (H)High-accuracy two-phase differential analog output
A-phase/B-phase analog, sine wave outputs
100μm output signal period (fixed) High S/N ratio and superior Lissajous characteristic for high resolution, in
combination with external interpolation circuit
Capable of outputting 9-bit data with a resolution of 100 µm in a range of up to 51.2 mm
Built-in terminal function with adjustable LED brightness and independent LED power supply
Built-in adjustment circuits can be used to adjust gain, binarization threshold, etc.
A serial interface compatible with SPI Mode 0 and Mode 3 enables adjustment circuit configuration andabsolute data readout
Supply voltage range 2.7 to 3.3V
Logic input tolerant function. Logic inputs are allowed up to 3.6 V
Low current consumption 8mA (typ)Easy positioning/installation
Reflow mounting (*confirm suitability of reflow conditions)[Typical Applications]Miniature actuators, piezo-actuators
Linear gauges
Chip mounters, PCB/FPC substrate processing, IC handlers & FA mounting/processing
Consumer equipment requiring precise position control, such as camera lenses
Position/speed control in applications requiring miniaturization and high accuracy

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Optical Encoder IC

2. Typical SM3414B Encoder Configurations
2.1. Linear Encoder Configuration and Alignment

SCALE

SM3414B

A linear encoder can be constructed using the SM3414B and a linear scale.
Position the linear scale with the boundary line between the incremental and absolute patterns on an axis passing
through the center of the IC chip center position and the LED center position (1.825 mm from the IC chip center and the
LED center).

[TOP VIEW]

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Optical Encoder IC

2.2. Cylindrical Rotary Encoder Configuration

Flexible scale

SM3414B

By using a flexible scale such as PET, it is possible to directly detect the rotation of a cylindrical rotating object, asshown in the drawing above. However, in the case of absolute patterns coded in the M code used in the recommended
scale, it is not possible to make a complete circle around the cylinder, except for certain diameters. Also, when only
incremental output is used, the pitch of the reflection pattern must be maintained at the joints between the scales. Thisrequires careful consideration by the customer.
For alignment of the SM3414B with the scale, see chapter 2-1.

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Optical Encoder IC

2.3. Scales for SM3414B
As described above, linear encoders using the SM3414B can be configured in combination with linear scales having
both incremental and absolute patterns.
Scales are not provided with the SM3414B; they must be acquired separately. The following manufacturers can supply
scales that can be used with the SM3414B.
2.3.1. Flexible PET scale
Flexible scales that use a PET substrate are more suitable. These can be supplied by the following manufacturer.
PET scales, in comparison with glass scales, are typically used for encoders in thin, narrow spaces.
[Flexible (PET) scale manufacturer]
Meltec Corporation sales Dept.
1038 Nagareyama, Nagareyama City, Chiba 270-0164, Japan
TEL: +81-4-7178-8800
URL: https://www.e-meltec.jp
E-mail: info@e-meltec.jp
Note that the SM3414B incremental signal output is designed for a detection period of 100μm so the scale should be
100μm pitch (reflective surface 50μm / non-reflective surface 50μm). Detection period cannot be changed even if thescale pitch is changed.
However, the SM3414B high-accuracy analog output signals can be configured to work with arbitrary resolution using
external interpolation circuits and counters.
Similarly, the absolute output of the SM-3414B is designed to operate on a scale with a 1-bit width of 100 µm. Do notchange the 1-bit width of the scale for absolute.
The absolute pattern should be a 100 µm wide pattern with 1 bit and a continuous 9-bit pattern indicating the positionon the scale. The SM3414B's absolute output photodetector is configured to read a 9-bit pattern, enabling it to output an
absolute position data of 512 positions. Our recommended scale pattern uses a method called M-code to encode theposition so that 512 positions can be specified on a single track. SM3414B is equipped with a function to convert
M-code into 9-bit binary numbers when outputting absolute position data. In addition to outputting the data as it is, theSM3414B can also output binary-converted position data.
For details on the M code conversion function, see data sheet '9.11. M code conversion function'.

[Recommended scale pattern]

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Optical Encoder IC

3. Operating Principles and SM3414B Characteristics
The main structural components are comprised by the SM3414B built-in LED and OEIC, and an external scale. Lightemitted from the LED is reflected with an intensity corresponding to the bright/dark pattern of the scale, and thereflected light creates a bright/dark pattern on the OEIC. The SM3414B realizes the functions of an incremental encoder
and an absolute encoder by monitoring this bright/dark pattern on the OEIC.
To monitor the pattern for incremental signals, the photodetectors (photodiodes) are arranged in an array on the surfaceof the OEIC at a pitch corresponding to 1/4 of the bright/dark cycle of the reflected light. This arrangement ofphotodetectors enables the output of two-phase sine signals with a phase shift of 90°. The photodetector array forincremental signals monitors several cycles of reflected light from the scale simultaneously and outputs the averagevalue. The SM3414B is designed with A-phase and B-phase outputs used to counterbalance the effects of variations
from perfect parallel movement as the photodiode array moves relative to the scale.
To monitor the bright /dark pattern for absolute data, 18 photodetectors (for 9 bits of the absolute signal) and 2 dummy
photodetectors at both ends (1 + 9 x 2 + 1) are arranged in an array at a pitch corresponding to 1/2 of the bright /darkpattern. The pattern for absolute data is monitored by the odd-numbered 9 photodetectors and the even-numbered 9
photodetectors, and is output as a 9-bit signal with a 1/2 cycle shift. Since two sets of 9-bit absolute data are generated
at positions that are half a cycle shifted, it is possible to select and read out the one with the more stable signal.

4. Reference Information about SM3414B Specifications
4.1. Reference information on package
4.1.1. Layout of SM3414B Internal Components
LED and OEIC are arranged as shown below.

[TOP VIEW]OEIC (built-in amp.)

Photodiode array(for Incremental signal))

Light shielding wall

LED

Photodiode array(for Absolute signal))

4.1.2. Environmental Data
The SM3414B is a lead-free, PVC-free (polyvinyl chloride), Halogen-free, and RoHS compliant product.

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Optical Encoder IC

4.2. Electrical Specifications Reference Information
4.2.1. Basic Connection
When using the SM3414B for the first time, make the necessary setup using the serial interface in the actual
environment in which it will be used.
The SM3414B should be used with bypass capacitors as shown below. Ceramic capacitors with good frequency
response are suitable as bypass capacitors. The 0.1 µF capacitor should be placed as close to the SM3414B as possible.

[Typical connection]

4.2.2. Setup and readout from the serial interface
To use the SM3414B, it is necessary to set various functions by writing to the internal registers using the serial interface
and to read information by reading the internal registers. The serial interface of the SM3414B supports SPI mode 0 andmode 3. For details on the serial interface, see data sheets '9.12. Serial interface functions' and '10.1. Timing chart Serialinterface'.

4.2.3. Adjustment of incremental signal output amplitude
To use the SM3414B, it is necessary to set various functions by writing to the internal registers using the serial interface[SM3414B Electrical Characteristics Excerpt]
Parameter
SymbolConditions
Min
Typ
Max
Unit

Incremental signal
output signal
amplitude

VAPP

PA, PB pins, 100kΩ load resistance (R),
ILED: 5mA
(RLED=100Ω, VLED_CON=0.5V)
I/V conversion gain: 1(register GA, GB [2:0]=0h *1)
DYAW=0, DPTCH=0, DROL=0, DGAP=0,
DCNTR=0

0.18

0.35

0.70

The SM3414B output signal specifications are outlined above.
This signal amplitude is based on an LED current of 5 mA (RLED = 100 Ω, VLED_CON = 0.5 V) on a standard scale
and an I/V conversion gain of 1x (GA [2:0] and GB [2:0] set value = 0). After adjustment of the gap, adjust the LED
current so that the signal amplitude of PA and PB is approximately 0.3 - 0.4 V. After that, change the GA[2:0] andGB[2:0] settings to obtain the desired amplitude of the PA and PB signals.
The incremental signals (PA and PB) are 2-phase analogue sine signals with a phase difference of 90° and are output
with the above signal width centered at 1/2 the voltage of VDD. One cycle of this incremental signal corresponds to ascale movement of 100 µm.

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Vp-p

SM3414B

Optical Encoder IC[LED Current Adjustment Function]
The SM3414 has a built-in LED element and LED driver, and the LED current can be adjusted by varying the voltage
applied to the LED_CON pin and the resistance value connected to the RLEDO pin.
In addition, the LED_VDD supply voltage is provided separately from the VDD pin. If the LED was driven fromonly the VDD voltage, the LED current control range is reduced by the forward voltage VF across the LED. However,a voltage higher than VDD can be applied to the LED_VDD pin to alleviate this problem.

[I/V Conversion Gain Setting Function]
The gain settings for the I/V conversion, which determines the amplitude of the incremental signals, can be adjusted via
the serial interface built into the SM3414B. By setting "001" to address [2:0] of the built-in register, the gain can be set
using the values set for phase A gain GA[2:0] and phase B gain GB[2:0].

4.2.4. Configurations about absolute output[Configuration overview]To use absolute output, several functions must be configured. This section gives an overview of the whole process. The
configuration of the absolute output is carried out in the following order, after the LED current has been adjusted bymeans of an incremental signal.
Configure the amplitude of the absolute signal.
Configure the threshold voltage for the binarization of the absolute signal.
Verification of the binarized absolute output.

[Configure the amplitude of the absolute signal]
Configures the function to specify internal signals to be monitored to enable monitoring of absolute signals andbinarization thresholds. By setting "0110" to the internal register MON_SEL[3:0] and "01001" to OUT_SEL2[4:0], thebinarization threshold signal (VCOMP) is output to the MON1 pin, the ninth photodetector output (ABS PD9) signal
will be output to the MON2 pin. Confirm that the amplitude of the ABS PD9 signal is about 0.1 Vp-p. The absolute I/Vconverter resistance adjustment function can be used to set the conversion voltage to 1x or 2x. If necessary, use theabsolute I/V converter resistance adjustment function to set the amplitude of the ABS PD9 signal to approximately 0.1
Vp-p.

[Configure the threshold voltage for the binarization of the absolute signal]
After configuring the amplitude of the absolute signal, use the VCOMP signal adjustment function to set the voltage forbinarizing the absolute signal. Move the scale in the region where the ABS PD output changes from dark to bright todark, and set the VCOMP signal so that the width of the voltage higher than the VCOMP signal of the ABS PD signal
and the width of the voltage lower than the VCOMP signal are approximately equal in length. By setting VCOMP tosuch a voltage, the binarized absolute signal can be read out with stable timing.
The voltage of the VCOMP signal can be calculated using the following formula. Refer to the datasheet for details.

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SM3414B

Optical Encoder IC[Waveforms when VCOMP is properly set]

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SM3414B

Optical Encoder IC[Waveform at low VCOMP setting][Verification of the binarized absolute output]
The internal registers MON_SEL[3:0], OUT_SEL1[4:0] and OUT_SEL2[4:0] are used to set the odd-numbered signalof ABS Co (binarized ABS_PD signal) to the MON1 pin and the even-numbered signal of ABS Co to the MON2 pin.
Move the scale in the same way as when setting the VCOMP signal, and confirm that the binarization switching timingof the even-numbered element of ABS Co does not overlap with the binarization switching timing of the odd-numberedelement.
Since correct absolute data cannot be read at the timing when the ABS Co signal is switched, if the switching timing of
the even-numbered and odd-numbered elements overlap, correct absolute data may not be read.
In such a case, set VCOMP again.

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Optical Encoder IC

4.2.5. Absolute data readout
Absolute data is read from the internal register via the serial interface. The internal register stores two sets of 9-bit data:
the data of the odd-numbered 9 elements of the ABS PD (Internal ABS Code1) and the data of the even-numbered 9
elements (Internal ABS Code2), which are binarized at VCOMP voltage.
To read the even-numbered side or the odd-numbered side of the absolute data is selected by the level of theincremental signal. If there is no yaw misalignment between the encoder IC and the scale mounting and no phasedifference between the incremental and absolute signals, the data of the odd element (Internal ABS Code1) will be read
during the period when the PB signal is Hi and the data of the even element (Internal ABS Code2) will be read during
the period when the PB signal is Lo. If misalignment exists in Yaw, the scale pattern is projected diagonally to the PD
for incremental signals and the PD for absolute signals, resulting in a phase difference between the incremental signals
and absolute signals. If there is any misalignment in Yaw, the scale pattern is projected diagonally to the PD for
incremental signals and the PD for absolute signals, resulting in a phase difference between the incremental andabsolute signals. In this case, it is necessary to select the appropriate PA or PB according to the amount of phase shift,and select readout of even or odd absolute data at Hi or Lo of the PA or PB. For details, please refer to the data sheet.
The data recorded on the NPC standard scale is binary data indicating positions encoded in M-code. The SM3414B has
a built-in M-code conversion function, and the data converted from the read M-code data to binary data is also stored in
the internal register at the same time, so select and read the data corresponding to the scale to be used. For the addressof the register to be read, refer to the data sheet.
When the voltage setting of VCOMP is appropriate, as shown in the figure below, the binarized Hi time and Lo time of
the ABS PD output are approximately the same, and stable absolute data can be read by switching the information to beread by the incremental signal level.

[Switching of data to be read out by PB level]

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Optical Encoder IC

5. Handling Precautions
Ensure the gray portion containing the LED and OEIC, shown in the
diagram, clean and free from dust and other contaminants.
If it is dirty, gently wipe the surface with a soft clean cloth dipped inmethanol or ethanol to remove all contaminants. The use of other liquids
or wiping vigorously may cause scratching, clouding, or otherwise
damage the surface of the encoder. Exercise caution when cleaning thedevice surface.
Avoid direct contact with the SM3414B and scale when handling,
installing, or adjusting.
Ensure that the operating temperature of any unit or housing containing
the SM3414B will not exceed the temperature specifications of thedevice.
Please note that there is the potential that strong localized light sources may affect the encoder output.
The light intensity of the SM3414B built-in LED does not exceed the value for Class 1 standard visible LED eye
safety as prescribed by IEC60825-1.

6. USAGE AND PRECAUTIONSThis product is designed and manufactured to the generally accepted standards of reliability as expected for use ingeneral electronic and electrical equipment, such as personal equipment, machine tools, and measurement
equipment. This product is not designed and manufactured to be used in any other special equipment requiringextremely high level of reliability and safety, such as aerospace equipment, nuclear power control equipment, medical
equipment, transportation equipment, disaster prevention equipment, security equipment.
If you wish to use this product in equipment requiring extremely high level of reliability, please contact our sales
department or representative in advance.
In the event that this product is used in such equipment, please take scrupulous care and apply fail-safe techniques
including redundancy and malfunction prevention in order to prevent damage to life, health, property, or infrastructureetc. in case there is some malfunction in the product.

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SM3414B

Optical Encoder ICThis Application Note is provided as a reference for product introduction and customer evaluation purposes for thisproduct. Typical characteristics and other values mentioned in this document are provided as reference data only todemonstrate principles and trends; this document does not include manufacturing tolerances and other characteristics
data. Devices should only be used after thorough evaluation under actual operating conditions.

Please pay your attention to the following points at time of using the products shown in this document.
1. The products shown in this document (hereinafter ”Products”) are designed and manufactured to the generally
accepted standards of reliability as expected for use in general electronic and electrical equipment, such as
personal equipment, machine tools and measurement equipment. The Products are not designed and manufactured
to be used in any other special equipment requiring extremely high level of reliability and safety, such as aerospaceequipment, nuclear power control equipment, medical equipment, transportation equipment, disaster prevention
equipment, security equipment. The Products are not designed and manufactured to be used for the apparatus thatexerts harmful influence on the human lives due to the defects, failure or malfunction of the Products.
If you wish to use the Products in that apparatus, please contact our sales section in advance.
In the event that the Products are used in such apparatus without our prior approval, we assume no responsibility
whatsoever for any damages resulting from the use of that apparatus.
2. NPC reserves the right to change the specifications of the Products in order to improve the characteristics orreliability thereof.
3. The information described in this document is presented only as a guide for using the Products. No responsibility is
assumed by us for any infringements of patents or other rights of the third parties which may result from its use. No
license is granted by implication or otherwise under any patents or other rights of the third parties. Then, we assume
no responsibility whatsoever for any damages resulting from that infringements.
4. The constant of each circuit shown in this document is described as an example, and it is not guaranteed about its
value of the mass production products.
5. In the case of that the Products in this document falls under the foreign exchange and foreign trade control law orother applicable laws and regulations, approval of the export to be based on those laws and regulations are necessary.
Customers are requested appropriately take steps to obtain required permissions or approvals from appropriate
government agencies.
6. When exporting customer’s products that use the Products, customers must comply with the "Foreign Exchange andForeign Trade Act" and other export-related laws and regulations, and follow the necessary procedures inaccordance with those laws and regulations. Do not use the Products in equipment whose sale is prohibited byexport-related laws and regulations ("JP Foreign Exchange and Foreign Trade Act" and "US Export Administration
Regulations", etc.). In addition, please do not sell the Products to users who are expected to use it for the above
equipment or companies in its supply chain. If a user who uses module parts and equipment using the Products is acompany suspected of violating human rights, please do not sell the above parts and equipment to that user.

SEIKO NPC CORPORATION
2-9-4, Taito, Taito-ku,
Tokyo 110-0016, Japan
TEL +81-3-6747-5300
FAX +81-3-6747-5303
https://www.npc.co.jp/
Email: sales@npc.co.jp

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